1. Field of the Invention
This invention relates to the refining of Mattes of non-ferrous metals, such as Mattes of copper, nickel, cobalt or lead.
2. Description of the Prior Art
The refining of molten mattes of non-ferrous metals, which mattes generally comprise iron sulfides and the sulfides of non-ferrous metals, is traditionally carried out in refractory-lined converters by blowing ordinary air or air slightly enriched with oxygen into the matte through single tube tuyeres embedded in the converter below the surface of the matte. The blast blown through the tuyeres cannot be enriched beyond about 36% of oxygen, however, without causing rapid erosion of the tuyeres and the surrounding refractory.
Workers in the art have recognized the desirability of increasing the oxygen content of the blast but this objective has only recently been achieved with the development of metallurgical processes employing multiple, concentric tube tuyeres which are protected against erosion by the injection of liquid or gaseous cooling agents through the outermost tubes of such tuyeres; refining agents and/or other additives are blown through the central or other inner tubes of the tuyeres. The liquid cooling agents blown in these new tuyeres include water, carbon dioxide in the liquid state, liquid hydrocarbons such as fuel oil, and the like. Exemplary of these multiple concentric tube tuyeres and their operation is U.S. Pat. No. 3,817,744 whose teachings are incorporated herein be reference. The tuyere disclosed in that patent comprises two concentric tubes but it is understood that, depending upon the metallurgical process involved, more than two concentric tubes advantageously may be used to form a tuyere.
U.S. Pat. No. 3,990,890 discloses a process for refining molten copper matte by means of a double tuyere which is cooled by the injection therethrough of a cooling agent. In one embodiment of the process disclosed in that patent, the cooling agent is a carbon-containing material, preferably fuel oil. In the process of U.S. Pat. No. 3,990,890, as well as in any process for refining non-ferrous metal matte, the atmosphere in the converter consists essentially of sulfur dioxide (SO.sub.2), also called sulfurous anhydride, and when nitrogen is present in the blast, nitrogen will also be present in the converter atmosphere. The component of principal interest in the atmosphere is, however, the SO.sub.2 produced by the oxidation reaction in the matte refining process.
In practicing the known non-ferrous matte refining processes, this SO.sub.2 atmosphere is contaminated by the introduction of other substances through the tuyeres, such as the carbon-containing material in the process of U.S. Pat. No. 3,990,890. To the extent that one wishes to produce by-products from the off gases, especially sulfuric acid, the presence of contaminants in those gases complicates such production because they cause the SO.sub.2 content of the off-gases to fluctuate.